1. Field of the Invention
The invention relates to a technology for a wireless communication terminal, such as a cell phone, to select one of the base stations before actually making a call.
2. Description of the Related Art
Conventionally, base stations and wireless controllers in a mobile wireless network transmit various information on systems and cells as annunciation information to a wireless terminal via a downlink common channel. On the other hand, the wireless terminal receives radio waves emitted from base stations, measures the receiving intensities, and detects a receiving intensity equal to or more than a threshold. Then, the wireless terminal selects an appropriate base station that can be called and connected thereto in the range of the location of the wireless terminal as a destination base station based on regulation information contained in the annunciation information and the detection results of the base station from which receiving at a receiving intensity equal to or more than the threshold is possible, and calls the base station.
On the other hand, when the base station and the wireless controller receive a call request transmitted from the wireless terminal, they secure a necessary resource and perform control to connect a core network and the wireless terminal. Then, the base station and the wireless controller notify the wireless terminal of a connection response, whereby establishing a calling connection.
The mobile communications technique described below is generally known. In a mobile communications system including a control station that performs control to exchange mobile communications, a plurality of wireless base stations connected to the control station, and a plurality of mobile stations that make communications via the wireless base stations within wireless zones of the respective wireless base stations, a downlink control channel signal from each wireless base station to the mobile station is provided with a congestion control signal frame having an annunciation signal for performing congestion control of overlapping wireless zones, and the mobile station determines a wireless zone of the wireless base station to be captured based on the annunciation signal (see, for example, Japanese Patent Application Laid-Open No. H09-23471).
The cell phone unit described below is generally known. In the cell phone unit to be used as a mobile station of a mobile communications system in which a service area is divided into a plurality of wireless zones corresponding to base stations partially overlapping each other, control channels exclusively used for communications connection control without interference with each other are assigned to the zones in addition to channels for communications as wireless channels between base stations and the mobile station for each wireless zone, and a control channel is selected when calling, called, and registering positions, the cell phone receives while successively switching the control channels, regards a base station received at a maximum level as an optimal destination base station by comparing intensities of the receiving levels, controls connection, and when the connection control is failed between the cell phone unit and the base station received at the maximum level, performs connection control by successively switching to base stations in descending order of receiving levels (see, for example, Japanese Patent Application Laid-Open No. H09-224281).
However, in the conventional connection methods, when congestion or failure occurs on the mobile wireless network side including the wireless controller, a resource necessary for the calling connection cannot be secured, so that the calling connection cannot be made. When no response is made from the mobile wireless network side to the wireless terminal, the wireless terminal transmits a call request to the base station again after a predetermined time elapses. Therefore, if the mobile wireless network side does not return a response to the wireless terminal due to a temporary resource shortage, it takes time to complete the calling.
Furthermore, it takes time for the wireless terminal to judge calling connection impossibility because it has no unit that makes the wireless terminal recognize the impossibility of calling due to the status in the mobile wireless network such as a temporary resource shortage. When a plurality of connectable base stations are present and cells of the base stations overlap each other, the resources of each station can be used. Namely, a plurality of resources are available for calling connection between the wireless terminal and a base station. In such a situation, first calling connection is made to a certain base station, and after a failure of the calling connection is detected, re-connection processing to another base station is performed, so that it takes time to complete the calling connection.